Stent fabrication method

ABSTRACT

A stent and a method for fabricating the stent are disclosed. The stent has an originally flat pattern and connection points where the sides of the flat pattern are joined. The method includes the steps of a) cutting a stent pattern into a flat piece of metal thereby to produce a metal pattern, b) deforming the metal pattern so as to cause two opposing sides to meet, and c) joining the two opposing sides at least at one point. Substantially no portion of the stent projects into the lumen of the stent when the stent is expanded against the internal wall of a blood vessel.

RELATED APPLICATIONS

This application is a continuation of Ser. No. 09/191,513, filed Nov.12, 1998, now U.S. Pat. No. 6,156,052 which is a continuation of Ser.No. 08/742,422, filed Oct. 30, 1996, now U.S. Pat. No. 5,836,964, whichis a continuation of Ser. No. 08/330,625, filed Oct. 27, 1994, nowabandoned.

FIELD OF THE INVENTION

The present invention relates generally to methods of fabricatingstents.

BACKGROUND OF THE INVENTION

Stents are known in the art. They are typically formed of a cylindricalmetal mesh which can expand when pressure is internally applied.Alternatively, they can be formed of wire wrapped into a cylindricalshape.

As described in U.S. Pat. No. 4,776,337 to Palmaz, the cylindrical metalmesh shape is produced by laser cutting a thin walled metal tube. Thelaser cuts away all but the lines and curves of the mesh.

The method of U.S. Pat. No. '337 is applicable for relatively large meshshapes and for meshes whose lines are relatively wide. However, for moredelicate and/or intricate shapes, the spot size of the laser is toolarge.

SUMMARY OF THE PRESENT INVENTION

It is, therefore, an object of the present invention to provide a stentfabrication method which can produce stents with relatively intricateand/or delicate designs.

The method involves first creating a flat version of the desired stentpattern from a piece of thin sheet metal. The flat pattern can beproduced through any suitable technique, such as etching the design intothe sheet metal, or by cutting with a very fine laser, should one becomecommercially available or by any other technique.

Once the sheet metal has been cut, it is deformed so as to cause itsedges to meet. To create a cylindrical stent from a flat, roughlyrectangular metal pattern, the flat metal is rolled until the edgesmeet. The locations where edges meet are joined together, such as byspot welding. Afterwards, the stent is polished, either mechanically orelectrochemically.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be understood and appreciated more fully fromthe following detailed description taken in conjunction with thedrawings in which:

FIG. 1 is a flow chart illustration of the stent fabrication method ofthe present invention;

FIGS. 2A, 2B and 2C are illustrations of three alternative stentpatterns to be etched, in accordance with the method of FIG. 1, into aflat sheet of metal;

FIG. 3 is an isometric illustration of a stent being deformed, useful inunderstanding the method of FIG. 1;

FIG. 4 is an isometric illustration of a stent formed from the method ofFIG. 1;

FIGS. 5A and 5B are side and top view illustrations, respectively, ofone connection location of the stent of FIG. 4;

FIG. 6 is a side view illustration of one connection location of thestent of FIG. 4 which is connected in a nail-like manner;

FIG. 7 shows a piece of sheet metal with a plurality of patterns made inaccordance with the invention;

FIG. 8 shows a detailed view of one of the patterns shown in FIG. 7;

FIG. 9 shows a detailed view of a pair of engagement troughs shown inFIG. 8;

FIG. 10 shows a detailed view of a pair of engaging protrusions shown inFIG. 8;

FIG. 11 shows the engagement troughs and engagement protrusions of FIGS.9 and 10 in the engaged position;

FIG. 12 shows a welding run practiced in accordance with the invention;

FIG. 13 is a detailed view of the welding run shown in FIG. 12;

FIG. 14 is a detailed view of a cell of a stent made in accordance withthis invention;

FIG. 15 is a detailed view of a cell made in accordance with thisinvention;

FIG. 16 shows a cell of a stent made in accordance with this invention;

FIG. 17 is an enlarged view of the cell shown in FIG. 16;

FIG. 18 is a cross-sectional view of a longitudinal member of a stentconstructed in accordance with this invention;

FIG. 19 is a cross-sectional view of a stent constructed in accordancewith this invention;

FIG. 20 is a perspective view of a stent constructed in accordance withthis invention;

FIG. 21 is a cross-sectional front view of an unexpanded stent made inaccordance with the invention;

FIG. 22 is a cross-sectional front view of the stent shown in FIG. 21after it has been expanded;

FIG. 23 is a cross-sectional front view of an unexpanded stent made bycutting a pattern in a tube; and

FIG. 24 is a cross-sectional front view of the stent shown in FIG. 23after expansion.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

Reference is now made to FIG. 1, which illustrates the stent fabricationmethod of the present invention and to FIGS. 2A, 2B, 2C, 3 and 4 whichare useful in understanding the method of FIG. 1.

In the stent fabrication method of the present invention, a stentdesigner first prepares a drawing of the desired stent pattern in a flatformat (step 10).

FIGS. 2A, 2B and 2C illustrate three exemplary stent pattern designs.The pattern of FIG. 2A has two types of sections 20 and 22. Each section20 has two opposing periodic patterns and each section 22 has aplurality of connecting lines 24. The pattern of FIG. 2A can be formedof any size; a preferable size is to have each section 20 be between 1and 6 mm wide and each section 22 have connecting lines 24 of 1-6 mmlong. At such sizes, the pattern of FIG. 2A cannot be cut using a lasercutting system.

The pattern of FIG. 2B is similar to that of FIG. 2A in that it also hassections 20 of opposing periodic patterns. The pattern of FIG. 2B alsohas connecting sections, labeled 30, which have a Z shape.

The pattern of FIG. 2C has no connecting sections. Instead, it has aseries of alternating patterns, labeled 32 and 34.

The patterns of FIGS. 2A, 2B and 2C optionally also have a plurality ofsmall protrusions 38 which are useful in forming the stent, as describedhereinbelow.

Returning to FIG. 1, in step 12, the stent pattern is cut into a flatpiece of metal (“sheet metal”). The metal can be any type ofbiocompatible material, such as stainless steel, or a material which isplated with a biocompatible material. The cutting operation can beimplemented in any of a number of ways, such as by etching, or bycutting with a fine cutting tool, or by cutting with a very fine laser,should one become commercially available.

If step 12 is implemented with etching, then, the process is designed tocut through the sheet metal. This process is known; however, for thepurposes of completeness, it will be briefly described hereinbelow.

The drawing of the pattern is reduced and printed onto a transparentfilm. Since it is desired to cut completely through the metal, thedrawing is printed onto two films which are joined together in a fewplaces along their edges. The sheet metal is covered, on both sides,with a layer of photoresist and placed between the two transparent,printed films. The structure is illuminated on both sides which causesthe portions of the photoresist which receive the light (which are allthe empty spaces in the pattern, such as spaces 26 of FIG. 2A) to changeproperties.

The sheet metal is placed into acid which eats away those portions ofthe photoresist which changes properties. The sheet metal is then placedinto an etching solution which etches away all material on which thereis no photoresist-removing solution which removes the photoresist,leaving the metal having the desired stent pattern.

In step 14, the metal pattern is deformed so as to cause its long sides(labeled 28 in FIGS. 2A, 2B and 2C) to meet each other. FIG. 3illustrates the deformation process. For cylindrical stents, thedeformation process is a rolling process, as shown.

If the protrusions 38 have been produced, after deformation of the metalpattern, the protrusions 38 protrude over the edge 28 to which they arenot attached. This is illustrated in FIG. 5A.

In step 16, the edges 28 are joined together by any suitable process,such as spot welding. If the protrusions 38 were made, the protrusions38 are joined to the opposite edge 28, either by welding, adhesive or,as illustrated in FIG. 6, with a nail-like element 40. FIG. 5Billustrates the connection of the protrusion to the opposite edge 28.Since protrusion 38 is typically designed to extend the width of oneloop 39, the pattern in approximately preserved. This is seen in FIG.5B.

Alternatively, the edges 28 can be brought together and joined in theappropriate places.

FIG. 4 illustrates a stent 31 formed by the process of steps 10-16 forthe pattern of FIG. 2A. It is noted that such a stent has connectionpoints 32 formed by the joining of the points 30.

Finally, the stent 31 is polished to remove any excess material notproperly removed by the cutting process (step 12). The polishing can beperformed mechanically, by rubbing a polishing stick having diamond duston its outside inside the stent 31. Alternatively, an electropolishingunit can be utilized.

FIG. 7 shows an alternative embodiment of the invention in which aplurality of patterns 120 are etched and cut into the sheet metal 121 aspreviously discussed. FIG. 8 is an enlarged view of one of the pluralityof patterns 120 shown in FIG. 7.

FIG. 9 is an enlarged view of one pair 127 of the plurality ofengagement troughs 128 and 129 shown in FIG. 8. FIG. 10 is an enlargedview of one pair 130 of the plurality of engagement protrusions 131 and132 shown in FIG. 8. The sheet metal 121 and each of the patterns 120 isprovided with a plurality of alignment apertures 122 and 122′ adapted toreceive sprockets (not shown) for precisely moving and maintaining theprecise alignment of the sheet metal 121 and the patterns 120 during thevarious stages of manufacturing. Each pattern 120 has a first long side123 and a second long side 124, a first short side 125, and a secondshort side 126. The first long side 123 is provided with a plurality ofpairs 127, 127′ and 127″ of engagement troughs 128 and 129 (shown ingreater detail in FIG. 9). Each pair 127, 127′ and 127″ of engagementtroughs has a first engagement trough 128 and a second engagement trough129. The second long side 124 is provided with a plurality of pairs 130,130′ and 130″ of engagement protrusions (shown in greater detail in FIG.10). Each pair 130, 130′ and 130″ of engagement protrusions is providedwith a first engagement protrusion 131 and a second engagementprotrusion 132. The pairs of engagement protrusions 130, 130′ and 130″are disposed substantially opposite the pairs of engagement troughs 127,127′ and 127″.

The engagement troughs 128 and 129 are disposed and adapted to receiveand engage the engagement protrusions 131 and 132 so that the alignmentof the stent is maintained when the pattern 120 is deformed and the flatsheet metal is rolled so that the first long side 123 and the secondlong side 124 meet each other to form a tube as shown in FIGS. 19 and20.

A bridge 133 of material is disposed between each pair 127, 127′ and127″ of engagement troughs 128 and 129. This bridge 133 impartsadditional stability and facilitates alignment during manufacturing andimparts additional strength to the welds of the finished stent asdiscussed below.

After the sheet has been rolled into a tubular stent and the engagementtroughs 128 and 129 have received the engagement protrusions 131 and132, means (not shown) are utilized to maintain the alignment and thebridge 133 is cut to leave two substantially equal parts. The bridge 133may be cut in a variety of ways well known to those skilled in the art,however, in a preferred embodiment, a laser is utilized. Engagementtrough 128 is welded to engagement protrusion 131 and engagement trough129 is welded to engagement protrusion 132 as shown in FIGS. 12 and 13.This may be accomplished in a variety of ways well known to thoseskilled in the art, however, in a preferred embodiment a plurality ofspot welds are utilized. In an especially preferred embodiment, aboutfive spot welds are used in each weld run as shown in FIGS. 12 and 13.The heat produced by the welding melts the cut bridge 133 material andthe material is drawn towards the engagement trough 128 or 129 to whichthe material is attached and is drawn into the welded area between theengagement trough and the engagement protrusion where the additionalbridge material becomes part of and imparts additional strength to theweld. The stent may then be finished as previously discussed.

FIG. 13 is an enlarged view of the welded area shown in FIG. 12. In apreferred embodiment, the weld run is offset from the point where theengagement trough and the engagement protrusion contact each other. Inan especially preferred embodiment, the weld run is offset about 0.01mm.

FIG. 14 is a detailed view of the pattern shown in FIG. 8. As shown inFIGS. 14 and 20, Applicants' invention can also be described as anexpandable stent defining a longitudinal aperture 80 having alongitudinal axis or extension 79 an a circumferential axis or extension105, including a plurality of flexible connected cells 50 with each ofthe flexible cells 50 having a first longitudinal end 77 and a secondlongitudinal end 78. Each cell 50 also is provided with a firstlongitudinal apex 100 disposed at the first longitudinal end 77 and asecond longitudinal apex 104 disposed at the second longitudinal end 78.Each cell 50 also includes a first member 51 having a longitudinalcomponent having a first end 52 and a second end 53; a second member 54having a longitudinal component having a first end 55 and a second end56; a third member 57 having a longitudinal component having a first end58 and a second end 59; and a fourth member 60 having a longitudinalcomponent having a first end 61 and a second end 62. The stent alsoincludes a first loop 63 defining a first angle 64 disposed between thefirst end 52 of the first member 51 and the first end 55 of the secondmember 54. A second loop 65 defining a second angle 66 is disposedbetween the second end 59 of the third member 57 and the second end 62of the fourth member 60 and is disposed generally opposite to the firstloop 63. A first flexible compensating member or flexible link 67 havinga first end 68 and a second end 69 is disposed between the first member51 and the third member 57 with the first end 68 of the first flexiblecompensating member or flexible link 67 communicating with the secondend 53 of the first member 51 and the second end 69 of the firstflexible compensating member or flexible link 67 communicating with thefirst end 58 of the third member 57. The first end 68 and the second end69 are disposed a variable longitudinal distance 70 from each other. Asecond flexible compensating member 71 having a first end 72 and asecond end 73 is disposed between the second member 54 and the fourthmember 60. The first end 72 of the second flexible compensating memberor flexible link 71 communicates with the second end 56 of the secondmember 54 and the second end 73 of the second flexible compensatingmember or flexible link 71 communicates with the first end 61 of thefourth member 60. The first end 72 and the second end 73 are disposed avariable longitudinal distance 74 from each other. In a preferredembodiment, the first and second flexible compensating member orflexible links 67 and 71 are arcuate. The first and second flexiblecompensating member or flexible links 67 and 71 are differentiallyextendable or compressible when the stent is bent in a curved directionaway from the longitudinal axis 79 of the aperture 80. (Shown in FIG.20.) The first member 51, second member 54, third member 57, and fourthmember 60 and the first loop 63 and the second loop 65 and the firstflexible compensating member or flexible link 67 and the second flexiblecompensating member or flexible link 71 are disposed so that as thestent is expanded the distance between the first flexible compensatingmember or flexible link 67 and the second flexible compensating memberor flexible link 71 increases and the longitudinal component of thefirst member 51, second member 54, third member 57 and fourth member 60decreases while the first loop 63 and the second loop 65 remaingenerally opposite to one another, the ends 68 and 69 of the firstflexible compensating member or flexible link 67 and the ends 72 and 73of the second flexible compensating member or flexible link 71 open soas to increase the variable longitudinal distance 70 between the firstend 68 and the second end 69 of the first flexible compensating memberor flexible link 67 and so as to increase the variable longitudinaldistance 74 between the first end 72 and the second end 73 of the secondflexible compensating member or flexible link 71. This compensates forthe decreasing of the longitudinal component of the first member 51,second member 54, third member 57, and fourth member 60 andsubstantially lessens the foreshortening of the stent upon itsexpansion. Upon expansion, the first flexible compensating member 67 andthe second flexible compensating member 71 impart support to the lumenbeing treated.

FIG. 15 shows the dimensions of an especially preferred embodiment ofthis invention. The deflection points, i.e., the first and second loops63 and 65 and the first and second compensating members 67 and 71, aremade wider than the first, second, third, and fourth members 51, 54, 57and 60 so that the force of the deflection is distributed over a widerarea upon the expansion of the stent. The deflection points can be madewider than the first, second, third and fourth members in differingamounts so that the deflection will occur in the narrower areas firstdue to the decreased resistance. In a preferred embodiment, the firstand second compensating members are wider than the first, second, thirdand fourth members and the first and second loops are wider than thefirst and second compensating members. One of the advantages of sizingthe first and second loops so that they are wider than the first andsecond compensating members is that the stent will substantiallycompensate for foreshortening as the stent is expanded. In theembodiment shown in FIG. 1., the first, second, third and fourth members51, 54, 57 and 60 have a width of about 0.1 mm. The first and secondloops 63 and 65 have a width of about 0.14 mm. The first and secondcompensating members 67 and 71 are provided with a thickened portion 75and 76 having a width of about 0.12 mm. Thus, in this especiallypreferred embodiment, the first and second loops have a width that isabout 40% greater and the first and second compensating members have awidth that is about 20% greater than the width of the first, second,third and fourth members.

FIGS. 16 through 20 show details of a stent constructed in accordancewith this invention.

Yet another advantage of Applicant's invention is shown in FIGS. 21 to24. For the sake of clarity, the dimensions and the degree ofdisplacement of the components of the stents shown in FIGS. 21 to 24 hasbeen intentionally exaggerated.

FIG. 21 is a cross-sectional front view taken along line A—A of theunexpanded stent made in accordance with applicants invention shown inFIG. 20. The unexpanded stent 200 of FIG. 21 is shown disposed in thelumen 202 of a blood vessel 201 prior to expansion. As previouslydiscussed, this stent is made by first cutting the stent pattern into aflat piece of sheet metal and then rolling the sheet metal into a tubeto form the tubular stent. As shown in FIG. 21 after rolling, the firstand second flexible compensating members 67 and 71 of the unexpandedstent tend to “flare out” in a direction away from the longitudinal axisor lumen of the stent. Thus, the flexible compensating members 67 and 71define outer diameters which are larger than the outer diameters definedby the remaining portions of the stent. FIG. 22 shows the stent of FIG.21 after it has been expanded in the lumen and against the internal wallof the blood vessel. As shown in FIG. 22, upon expansion of theunexpanded stent toward the wall of the blood vessels, the walls of theblood vessel imparts a mechanical force to the first and second flexiblecompensating members 67 and 71 and the compensating members move towardthe longitudinal axis or lumen of the stent until they are substantiallyin registry with the remaining portion of the stent. Thus, the lumen ofthe expanded stent is substantially circular when viewed in crosssection with substantially no portion of the expanded stent projectinginto the lumen or towards the longitudinal axis of the expanded stent.

FIG. 23 is similar to FIG. 21 except that the pattern has been cut intoa tubular member using conventional methods of making stents. As shownin FIG. 23, the flexible compensating members do not flare out away fromthe longitudinal axis of the unexpanded stent 203. Upon the expansion ofthe stent shown in FIG. 23 toward the walls of the blood vessel 201, theflexible compensating members 67′ and 71′ tend to “flare in” and projectinto the lumen 204 of the expanded stent 203.

FIG. 24 shows the stent 203 of FIG. 23 after it has been expanded in alumen 204 of a blood vessel 201. The flexible compensating members 67′and 71′ are not in registry with the remaining portions of the stent anddefine a diameter smaller than the diameter of remaining portions of thestent. These projections into the lumen of the stent create turbulencein a fluid flowing through the longitudinal axis of the expanded stentand could result in clot formation.

It will be appreciated by persons skilled in the art that the presentinvention is not limited to what has been particularly shown anddescribed hereinabove. Rather the scope of the present invention isdefined only by the claims which follow.

What is claimed is:
 1. An expandable stent having a longitudinal lumencomprising: a) a first long side and a second long side, said first longside provided with a plurality of pairs of engagement troughs, saidsecond long side provided with a plurality of pairs of engagementprotrusions, said plurality of pairs of engagement troughs and saidplurality of pairs of engagement protrusions disposed substantiallyopposite each other, said plurality of engagement troughs sized anddisposed to receive and engage said engagement protrusions, saidengagement troughs attached to said engagement protrusions.
 2. The stentof claim 1, said stent adapted so that upon expansion of said stentagainst the internal wall of a vessel substantially no portion of saidstent projects into said lumen.
 3. An expandable stent having alongitudinal lumen, comprising: plurality of portions connected by aplurality of flexible compensating members projecting from the externalsurface of said stent when said stent is unexpanded and said flexiblecompensating members substantially in registry with the remainingportions of said stent when said stent is expanded against the internalwalls of a blood vessel.
 4. The stent of claim 3, wherein said stent isformed from a substantially flat sheet.
 5. The stent of claim 3, whereinsaid flexible compensating members are arcuate.
 6. The stent of claim 3,further having a longitudinal lumen, wherein said flexible compensatingmembers are differentially extendable or compressible when the stent isbent in a curved direction away from a longitudinal axis of thelongitudinal lumen.
 7. The stent of claim 3, further having alongitudinal lumen, and comprising a stent pattern comprising aplurality of flexible connected cells, each of said flexible cellscomprising: a) a first member having a longitudinal component having afirst end and a second end; b) a second member having a longitudinalcomponent having a first end and a second end, c) a third member havinga longitudinal component having a first end and a second end; d) afourth member having a longitudinal component having a first end and asecond end; e) a first loop defining a first angle disposed between saidfirst end of first member and said first end of second member; f) asecond loop defining a second angle disposed between said second end ofsaid third member and said second end of said fourth member, anddisposed generally opposite to said first loop;  wherein said pluralityof flexible compensating members include, for each of said flexiblecells: (i) a first flexible compensating member or flexible link havinga first end and a second end disposed between said first member and saidthird member, said first end of said first flexible compensating memberor flexible link communicating with said second end of said first memberand said second end of said first flexible compensating member orflexible link communicating with said first end of said third member,said first and said second ends disposed a variable longitudinaldistance from each other; (ii) a second flexible compensating member orflexible link having a first end and a second end disposed between saidsecond member and said fourth member, said first end of said secondflexible compensating member or flexible link communicating with saidsecond end of said second member and said second end of said secondflexible compensating member or flexible link communicating with saidfirst end of said fourth member, said first and said second endsdisposed a variable longitudinal distance from each other, said firstand said second flexible compensating member or flexible linkdifferentially extendable or compressible when said stent is bent in acurved direction away from the longitudinal axis of said longitudinallumen; and g) said first, said second, said third, and said fourthmembers and said first and said second loops, and said first and saidsecond flexible compensating member or flexible links disposed so thatas said stent is expanded the distance between said first and saidsecond flexible compensating member or flexible links increases and thelongitudinal component of said first, second, third and fourth membersdecreases while said first and said second loops remain generallyopposite to one another, the ends of said first and said second flexiblecompensating member or flexible links open so as to increase saidvariable longitudinal distance between said first and said second endsof said first flexible compensating member or flexible link and so as toincrease said variable longitudinal distance between said first and saidsecond ends of said second flexible compensating member or flexible linkso as to compensate for the decreasing of the longitudinal component ofsaid first, second, third, and fourth members and substantially lessenthe foreshortening of said stent upon its expansion.
 8. The stent ofclaim 7, wherein said stent pattern has a first long side and a secondlong side, said first long side provided with a plurality of pairs ofengagement troughs, said second long side provided with a plurality ofpairs of engagement protrusions, said plurality of pairs of engagementtroughs and said plurality of pairs of engagement protrusions disposedsubstantially opposite each other, each of said plurality of pairs ofsaid engagement troughs comprising a first engagement trough and asecond engagement trough, said engagement troughs attached to saidengagement protrusions.
 9. The stent of claim 8, wherein said engagementprotrusions are attached to said engagement troughs via an adhesive. 10.The stent of claim 8, wherein said engagement protrusions are attachedto said engagement troughs by a nail-like element.
 11. The stent ofclaim 7, said stent pattern is adapted so that upon expansion of saidstent against the internal wall of a vessel substantially no portion ofsaid stent protrudes into said longitudinal lumen of said stent.
 12. Anexpandable stent having a longitudinal lumen, comprising: A plurality ofportions connected by a plurality of flexible compensating memberswherein substantially no portion of said stent projects into said lumenwhen said stent is expanded against the internal wall of a blood vessel.13. The stent of claim 12 wherein said stent is formed from asubstantially flat sheet.